The present invention relates to a method of checking that a system recovering vapour emitted in a liquid dispensing installation, in particular when dispensing fuel to the interior of a motor vehicle tank, is operating correctly.
Fuel dispensing installations conventionally comprise a fuel storage tank, a pipe for dispensing liquid incorporating a delivery pump enabling the fuel to be circulated between the storage tank and a dispensing gun at a liquid delivery rate QL, as well as counting means connected into the liquid dispensing pipe and fitted with a liquid measuring unit linked to a pulse generator or coder enabling a computer to ascertain the volume and price of the fuel dispensed, which then appear in plain text on a display.
For reasons of safety (risk of explosion) and environmental protection, installations of this type ate generally fitted with a system for recovering vapour emitted when the tank is being filled; such a system comprises a pipe for recovering vapour incorporating a recovery pump which enables the vapour to be circulated between the dispenser gun and the storage tank at a vapour delivery rate QV when the tank is being filled.
In order for a system of this type to operate efficiently, the delivery rate of the vapour QV at any instant must be approximately the same as the liquid delivery rate QL.
In order to achieve this performance, the recovery system is fitted with control means which are able to maintain this balance.
In smaller installations having only one or two dispenser guns, these control means are provided in the form of simple means whereby the vapour delivery rate QV is calibrated beforehand on the maximum liquid delivery rate QLmax, which is generally in the order of 40 litres per minute.
In larger, more sophisticated installations, the control teams consist of an electronic control unit fitted with a microprocessor, connected to counting means which supply the value of the liquid delivery rate QL instantaneously and co-operate either with the recovery pump if it is of the variable delivery type and hence operates a variable delivery rate, or with an electronically operated control valve connected into the vapour recovery pipe if the recovery pump operates at a fixed rate. In a system of this type, the values governing opening of the electronically operated control valve or the speed of the recovery pump corresponding to a vapour delivery rate QV are stored in the memory of the microprocessor during the initial calibration process.
Vapour recovery system of the type outlined above are generally efficient immediately after they have been calibrated. After a period in service operation, however, the results become leas certain, not to say totally erratic.
This situation is generally attributable to ageing of the equipment: wear on the pumps, clogged pipelines, stretching in the belts leading to a reduction in pumping rates, blocked pumps, etc.
Currently used installations are not fitted with units to detect when operation is poor and incapable of maintaining equality between the liquid delivery rate QL and the vapour delivery rate QV and the period between two service inspections on the installation may be very long (one to three years), which represents a source of pollution in particular and is therefore harmful to the air quality.
It should be pointed out that an earlier document, U.S. Pat. No. 5,332,008, discloses (column 4, lines 13-18) a fuel dispensing installation incorporating a vapour recovery system which is fitted with a sensor detecting operation of the recovery pump, which means that the speed normally expected of this pump can be checked and distribution disabled in the event of an anomaly.
However, this detection system is not always able to react if the pump is exhibiting mechanical wear (changes in its characteristics), which may render it incapable of attaining a vapour delivery rate QV equal to the liquid delivery rate QL.
The same applies if the suction or delivery pipes of the recovery pump become partially or totally blocked (due to encrustation or by accidental means); if an installation is fitted with an electronically operated control valve, its timing will initially have been programmed after calibration, thereby preventing an adequate delivery rate from being achieved and the vapour delivery rate QV is always lower than the liquid delivery rate QL and may even fall to zero under extreme circumstances unless the detection system disclosed in this earlier publication triggers an alarm to indicate that there is a malfunction.
In document U.S. Pat. No. 5,857,500, it was also suggested that automatic checks be made on the recovery pump for wear, when not dispensing fuel, by means of a command issued to electronically controlled valves upstream and downstream of the pump to be checked and to do so by providing two pressure sensors to measure the active or negative pressures attained when the pump is rotating. The pressures measured during an opening/closing cycle of the electronically controlled valves can be compared with the measurements taken when the system was installed in order to determine the extent of wear on the recovery pump.
According to this earlier document, another test was to measure the drop in pressure on the auction side what dispensing In order to evaluate the degree of encrustation or blockage at the level of the vapour recovery pipe.
However, these are nothing more than pressure measurements which depend both on an instantaneous delivery rate and resistance in the line in which changes are evaluated as compared with the initial situation as recorded on the date of installation.
The objective of the present invention in to remedy the above-mentioned disadvantages by proposing a method of checking that the system used to recover vapour in a liquid dispensing installation, in particular when dispensing fuel to the interior of a motor vehicle tank, is operating correctly, providing a reliable indication of any malfunction in the vapour recovery system, regardless of the source of this malfunction
Accordingly, the method proposed by the invention is characterised in that:
the vapour delivery rate QV is constantly detected by detection means,
the value of the vapour delivery rate QV thus detected is transmitted to comparison means which compare it with a value of the liquid delivery rate QL and
if the result of this comparison is outside a predetermined range, which may or may not be adjustable, an alarm is triggered in order to indicate a malfunction.
In a first embodiment of the invention adapted to a vapour recovery systen having an electronic control unit co-operating with an electronically operated control valve or a variable delivery pump, the value of the liquid delivery rate QL determined by the counting means is constantly transmitted to the comparison means and it is compared with the value of the vapour delivery rate QV detected by the detection means.
It should be pointed out that in the case of this embodiment, the vapour delivery rate QV is compared with the liquid delivery race QL by the electronic control unit if this function has been programmed in the microprocessor incorporated therein, although this is not always the case with existing systems which would have to be modified accordingly.
In addition, if the microprocessor of the electronic control unit is able to interact with the computer of the counting means, the alarm could also be transmitted via this computer to the service station manager or remotely transmitted to a maintenance company which could then respond more rapidly.
In a second embodiment of the invention adapted to a simplified recovery system which does not have an electronic control unit and in which the control means correspond co a prior calibration of the vapour delivery rate QV to the maximum liquid delivery rate QLmax, the maximum value QLmax of the liquid delivery rate QL in stored in the comparison means and the value of the vapour delivery rate QV detested by the detection means in compared with this maximum value QLmax,
With regard to this second embodiment, it should be pointed out that the threshold triggering the alarm indicating a malfunction may be based on a specific mechanical structure or alternatively on a fluid-related phenomenon.
By virtue of another feature of the invention, also relating to this second embodiment, the alarm indicating a malfunction is disabled for a predetermined period after the liquid dispensing pump has been activated and it is then re-activated for a predetermined time so that it can be disabled again until the end of the tank-filling operation.
It is often necessary to disable the system in this manner, particularly at the end of the filling protest when the user finishes the operation at a low delivery rate or alternatively at the start of filling: accordingly, the invention enables the alarm to be disabled for a time to after detecting the first pulses indicating the start of liquid delivery QL, after which the alarm may be active for a time ti and finally disabled again after t0+t1 until the end of filling, which is of particular advantage in the case of pre-payment.
It should be pointed out that the fuel dispensing system can be fitted with an additional device such as a calibrated detector (for example a detector with paddles or vanes which move with the liquid flow QL) co-operating with an alarm switch which allows the alarm to be disabled if the liquid delivery rate QL is below the maximum liquid delivery rate QLmax.
As a result of a preferred feature of the invention, the detection means and the comparison means are selected so that any fault in these means will also trigger the alarm to indicate a malfunction.
This essential characteristic, which corresponds to an active safety system, allows the alarm to be triggered to indicate a malfunction irrespective of the source of this malfunction.
It should be pointed out that a delivery rate measurement based on measuring a pressure difference at the terminals of a membrane by means of a pressure sensor susceptible to drift, can nor be regarded as an active safety system of the type mentioned above whereas a detector, on the other hand, transmitting an alternating signal depending on the flow rate will almost always be seen as an active safety feature.
The invention also relates to an installation enabling the above-mentioned method to be implemented.
For the purpose of the invention, such an installation conventionally comprises:
a storage tank for the fuel to be dispensed,
a dispensing pipe for the liquid incorporating a delivery pump which enables the fuel to be circulated between the storage tank and a dispenser gun at a liquid delivery rate QL,
a vapour recovery pipe incorporating a recovery pump enabling the vapour emitted when filling the tank to be circulated between the dispenser gun and the storage tank at a vapour delivery rate QV,
counting means connected into the liquid dispensing pipe and having a liquid measuring unit linked to a pulse generator or coder so that a computer can ascertain the volume and price of the fuel dispensed, which will appear in plain text on a display and
control means enabling the vapour delivery rate QV to be held more or less at the same level as the liquid delivery rate QL at any instant.
For the purpose of the invention, this installation is characterised in that it comprises.
detection means enabling the vapour delivery rate QV to be constantly detected,
comparison means sensitive to the vapour delivery rate QV detected by the detection means and enabling this delivery rate QV to be compared with a value of the liquid delivery rate QL and
alarm means which, if the result of this comparison is outside a predetermined range, which may be or not be controllable, triggers an alarm alerting either to a fault in the vapour recovery system, in particular the control means, or a failure of the detection means or comparison means.
In accordance with the invention, the signal transmitted by the alarm means may be an optical signal or an electric signal emitted, as is the case, by a detector mounted on the tracker of a magnetic member.
It should be pointed out that the alarm may be given simply by interrupting the delivery of fuel.
The configuration of the detection means and the comparison means may vary to a large degree depending on the characteristics of the fuel dispensing installation and in particular depending on whether it is adapted to the first or second of the embodiments mentioned above.
By way of example and in accordance with another feature of the invention the detection means may be a flow detector of the fluid oscillator type such as a flow meter with an oscillating jet or an eddy flow meter.
In flow meters of this type, the alternating passage of the vapour jet in front of two orifices connected to a differential pressure sensor, for example, generates an alternating pressure detected by the sensor and amplified; only the frequency of the phenomenon is taken into account not its amplitude, which is susceptible to shifts in the pressure sensor. The frequency F of the signal emitted by the amplifier is directly proportional to the vapour flow rate; this frequency F compared with a pre-established reference frequency FO enables an alarm to be triggered, for example as soon as 1.1xe2x89xa6F/F0xe2x89xa60.9.
If the vapour recovery system in managed by a microprocessor, this comparison operation is easy and can be set up without any additional expense.
An operating fault in the sensor or the amplifier or any damage at the orifices at which the differential pressure measurement is taken correspond to an absence of any signal and hence to a zero flow rate. Consequently, any malfunction in a detection system of this type will cause an alarm to be triggered and is therefore also an active safety feature.
By virtue of another feature of the invention, the detection means are provided in the form of a mechanical oscillator.
A flow detector based on the movement of a mechanical oscillator whose frequency depends on the flow rate can also be regarded as an active safety system for the same reasons as those described above.
In accordance with another characteristic of the invention, the detection means are provided in the form of a constrictive element, in particular of the Venturi type, connected to a system that is sensitive to pressure and provided with a mechanical memory.
In accordance with another feature of the invention, the detection means ray be a constrictive member, in particular of the venturi type, which do not operate except above a f low threshold which may or tray not be adjustable.
In accordance with another feature of the invention, the detection means are a turbine.
A turbine gives accurate information about flow rate and above all enables an alternating signal to be generated, for example as its vanes pass in front of a detector (optical, field-effect, etc.), and is therefore an active safety feature.
Any slowing down due to untimely friction or blockage of the turbine triggers an alarm. Clearly, reliable usage of a turbine would only be conceivable if dust had been totally removed from the gases.
By virtue of another feature of the invention, the detection means are provided in the form of a paddle or obstacle.
In accordance with another feature of the invention, the detection means co-operate with alarm means via optical transmission units.